What exactly adult content are you pertaining too? If it still has something related to pornography even without visual images related to, I don't think you should have them on your board since it's still a part of an illicit content.

Illicit contents

Forums that welcomes or promotes warez, piracy, hacking, cracking, spamming, attacks against networks or servers, pornography, racial hatred, crimes against humanity, inappropriate activities on the servers, or any other actions which violate any applicable laws, are not allowed. Any forum which contains texts, links, pictures, animations, videos or any other content recognized as illegal will be deleted without notice or warning. Forumotion.com reserves the right to delete any accounts or forums considered like not conform to the rules quoted here or specified in Forumotion.com or in the international website rules according to the international internet law. Any illegal content or act can or would be reported to the concerned services and prosecuted.

If it is sexually explicit literature then it is still pornography and would be against TOS.

Definition of PORNOGRAPHY1: the depiction of erotic behavior (as in pictures or writing) intended to cause sexual excitement 2: material (as books or a photograph) that depicts erotic behavior and is intended to cause sexual excitement 3: the depiction of acts in a sensational manner so as to arouse a quick intense emotional reaction.